<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<meta name="Generator" content="Microsoft Word 15 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0in;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri",sans-serif;}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:#0563C1;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:#954F72;
text-decoration:underline;}
span.EmailStyle17
{mso-style-type:personal-compose;
font-family:"Calibri",sans-serif;
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri",sans-serif;}
@page WordSection1
{size:8.5in 11.0in;
margin:1.0in 1.0in 1.0in 1.0in;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-US" link="#0563C1" vlink="#954F72">
<div class="WordSection1">
<p class="MsoNormal">I am trying to understand the cost returned by ComputeSpeculationCost function in SimplifyCFG. It appears even when it returns TCC_Expensive (which means “prohibitively expensive”), the caller may proceed with a transform, because TCC_Expensive
is not really a high cost, but its value is 4.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">For example when DominatesMergePoint calls this, it may still move ahead because TCC_Expensive cost may be less than CostRemaining. Looking thru the history, it appears this behavior changed with r228826 (<a href="http://llvm.org/viewvc/llvm-project?view=revision&revision=228826">http://llvm.org/viewvc/llvm-project?view=revision&revision=228826</a>),
when this API was moved to use TargetTransformInfo for cost analysis instead of the hard-coded cost estimates.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Is this a bug?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks,<o:p></o:p></p>
<p class="MsoNormal">Gautam<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
</div>
<DIV>
<HR>
</DIV>
<DIV>This email message is for the sole use of the intended recipient(s) and may
contain confidential information. Any unauthorized review, use, disclosure
or distribution is prohibited. If you are not the intended recipient,
please contact the sender by reply email and destroy all copies of the original
message. </DIV>
<DIV>
<HR>
</DIV>
</body>
</html>